let m = new Map();
m.set('first', 1);
m.set('second', 2);
m.set('third', 3);
console.log(m);
m.forEach((x, y) => {
    console.log('key: ' + x + '  value: ' + y);
});
for (let key of m.keys()) {
    console.log('keys: ' + key);
}
for (let value of m.values()) {
    console.log('value: ' + value);
}
console.log(m.has('first'));
